Slightly flummoxed by the apparent lack of a front door, I ask a man standing nearby if he can help me find the entrance to London's latest boutique hotel. He looks a little confused. 'You want skunk?' he offers. 'Pills? Coke?'

He's probably thinking I'm already off my head to be looking for a smart new hotel outside KFC on the corner of Brixton's Coldharbour Lane, probably Britain's least salubrious street. But somewhere in the building is Dex, apparently a cool mix of private members club, restaurant and hotel. The website had made it look incredibly swish, and promised the chance to 'glide up a marble staircase and into an altogether different kind of place'.

I do eventually get in, but there's not much gliding involved. I ask at the bar of the Prince, a pub next door to KFC, which is also owned by Dex. The barman leads me behind the bar, up a narrow back staircase, past the kitchen, a lot of exposed wiring and through the main first-floor club room. This is where the members' club is supposed to be, but tonight it is deserted, and the barman explains he doesn't think it has really taken off yet.

The eight rooms are on the second floor. Mine, the master suite, is pretty funky - with a carved four-poster bed, wallpaper whose palm motif chimes with a potted palm in the corner, interesting dark wood furniture and a huge whirlpool bath. It's large and airy, with four windows in the bedroom, and at £150 a night would be good value for London. Except, that is, for the musty smell, the empty mini-bar, the dirty bath mats, the half-used shower gel and shampoo, and the few meagre sheets of toilet roll left forlornly in the holder.

When I was at school my friend John fell asleep in some nightclub toilets and woke up to find he was locked inside for the whole night. As I wander around Dex I understand how he must have felt - there's not a single other person to be seen, and no sign of a restaurant, nor anywhere to have breakfast.

This total lack of service and atmosphere is a terrible shame, because this is an absolutely beautiful building and could be a great hotel. Dating from the 1930s, there are lots of original Art Deco touches, some gorgeous gilded light fittings, high ceilings and wide corridors. There's also a wonderful roof terrace on two levels, with wooden loungers, a hot tub and great views over south London. Tonight, it's empty and wet, but on a summer's night this could be a sensational party venue.

Back in the empty first-floor room, I find some flyers on a windowsill touting the regular club nights which take place here and go on until 6am. On those nights, this place must make sense - what better after a full-on night out than to avoid doing battle with the night buses and simply walk upstairs to a classy bedroom. If you've been on it till 6am, you probably won't notice the dirty bath mat either. You can lie in all the next day too - checkout isn't until 5pm.

But as a proper hotel, rather than a post-club crash pad, Dex has a very long way to go. After a night spent listening to sirens and shouting, I creep back through the empty club and let myself out.

What we liked: the stunning roof terraceWhat we didn't like: the lack of serviceThe cost: doubles from £100The verdict: great idea, terrible execution